I don't quite agree with this oft-repeated claim.
Apparently statistics show that few incidents of cyclist harm are due to RLJing by the cyclist. I would like to ask a lot of hard questions about those stats before I leaned any weight on them.
Even if they are sound, I feel that it is outweighed by the stress RLJing puts on everyone else, cyclists included. Being careful is good, but the more hazards one has to be careful about the sooner it is that you are likely to succumb to one. If I can't reasonably expect to cross an intersection on green without having to avoid RLJ-ing pillocks, or having to avoid motorists swerving to avoid same, then I am sorry, I see a greater risk to me there.
It may feel safer for the RLJ-ers getting ahead of the traffic, but it is just pushing the risk onto others -fellow cyclists and pedestrians.
Also, the prevalence of RLJing erodes the general climate of observance of the Highway Code, and encourages others (motorists included), to feel they can copy.
Finally, it makes motorists hate us, encouraging the lunatic fringe to rant, throw things, close pass, or even run us off the road, and for the rest to share in a general climate of disrespect for cyclists. (Yes they do that anyway, but its one more provocation we can afford not to give).
In my opinion, RLJing is a direct threat to me as a rider, no matter how 'safe' it may supposedly be for those doing it.